The present invention generally relates to methods of monitoring the health of plants. More particularly, this invention relates to aerial imaging of vegetation to determine and monitor plant health.
Various technologies have been used in the past to measure temperature of plant leaves. For example, U.S. Pat. No. 7,058,197 uses visual light reflectance to generate NDVI images. This patent relies on reflected light from the sun, and therefore teaches that the optimum time for image acquisition using the disclosed process is within two hours of “solar noon” and on cloudless days. This makes it very impractical for a commercial application. In particular, this patent discloses                Aerial imagery was collected four times throughout the growing season. The image dates correlated with bare soil, VI2, VT, and R4 crop stages (see section on “Resolutions in Remote Sensing”). The aerial imagery was flown with digital cameras with an array size of approximately 1500 pixels wide and 1000 pixels in the along track dimension. The digital systems were 8-bit systems and were collected and stored on an on-board computer in a Tagged Image Format (TIF). Four bands were collected representing the blue, green, red, and near infrared portions of the electromagnetic spectrum (see section on “Spectral Nature of Remote Sensing”). The cameras were aligned in a two-by-two matrix and were rigid mounted (pseudo-bore sited) with the lenses focused [sic] on infinity. The imagery was flown at approximately 5000 feet above ground level (AGL) to produce a spatial resolution of approximately one meter by one meter (see section on “Resolutions in Remote Sensing”). The digital cameras have square pixels and are not interlaced during image acquisition. The optimum time for image acquisition was two hours before or two hours after solar noon (see section on “Resolutions in Remote Sensing”). Images were not acquired during times of poor atmospheric conditions (haze, rain, clouds). No cloud shadows were acceptable in the imagery.        
In addition, it appears that the methodology disclosed by U.S. Pat. No. 7,058,197 is only able to indicate that a problem exists after a plant has actually changed its structure, as indicated by its color. In many cases, this is too late to take corrective action. Column 6 of U.S. Pat. No. 7,058,197 describes the extent of the methodology's capability as follows:                The third major division of the electromagnetic spectrum ranges from around 1500 nanometers to approximately 3000 nanometers and is referred to as the middle-infrared. It is this portion of the electromagnetic spectrum where moisture plays a dominant role. Although other factors such as organic matter, iron content, and clay content have an effect, moisture appears be the primary mechanism affecting reflectance. More specifically, the higher the moisture content, the lower the reflectance. As objects lose moisture or begin to dry, their reflectance in this portion of the electromagnetic spectrum increases. While this concept has been proven in a laboratory setting, applying this concept in practice has been somewhat evasive.        
As another example, U.S. Pat. No. 6,597,991 uses thermal imaging to detect water content in leaves for irrigation purposes. This patent is reliant on obtaining actual temperatures and using ground-based references for calibration. Arguably, a significant disadvantage of U.S. Pat. No. 6,597,991 is its reliance on extremely accurate temperature measurements so that the need for irrigation can be determined. Such a requirement necessitates an extra step and additional costs associated with the calibration. U.S. Pat. No. 6,597,991 does not appear to contain a reference to the detection of disease in very early stages.
In view of the above, it can be appreciated that there are certain problems, shortcomings or disadvantages associated with the prior art, and that it would be desirable if an improved method were available for aerial monitoring of plant health that does not rely on sensing reflected light or ground-based measurements.